Results of the recent Merck Ad5 vaccine trial suggest that our current understanding of protective immunity in HIV infection is severely limited. As increasing evidence indicates that the early events in HIV infection determine the long-term outcome of this disease, integrated studies of acute HIV pathogenesis are warranted to identify the critical components of innate and adaptive immunity that ultimately impact viral control. While current HIV vaccine design strategies focus on inducing stronger and broader T cell responses, little consideration has been directed towards the selection of specific vaccine antigens and the quality of the antiviral immune response. We hypothesize that current vaccine approaches are not sufficiently focused with respect to antigen selection to induce the most protective and functional early T cell responses against the most critical regions of the virus, and that far more concerted efforts, both immunologically and virologically, is necessary to identify these critical regions. This Program Project Grant (PPG) represents an outgrowth of a long and productive effort to understand the immunologic and virologic events related to acute infection. During the previous period of support through the AIEDRP, we established an extensive cohort of persons with acute infection and identified key insights into the immunology and virology of acute infection. Here we propose to build upon this work to identify factors that we believe are fundamental to a protective antiviral immune response, including regions of HIV: (1) that are immunodominantly targeted by CD8+ T cell responses during acute HIV infection that exhibit strong antiviral activity. (2) that are rapidly processed into epitopes and presented by HLA alleles. (3) that are refractory to viral escape, or escape only at the cost to replicative fitness: and (4) that preferentially bind to stimulatory myelomonocytic receptors on myeloid dendritic cells. We believe that these vulnerable regions of HIV need to be identified to allow for the rational selection of specific antigenic regions for inclusion into a vaccine. In addition, it will be critical to determine how to best focus the vaccine-induced immune response against these regions, which will require an understanding of (5) what types of innate responses correlate with the induction of adaptive T cell responses with strong antiviral activity, and (6) what modifications to flanking regions of epitopes will enhance the antigen processing and presentation of the critical regions of HIV. This PPG application will provide highly relevant data for vaccine design regarding the earliest protective innate and adaptive immune responses, the parameters that define effective functional immune responses, and how these shape viral evolution and viral fitness. PROJECT 1: Recognition of HIV-1 by Innate Immunity Receptors During Primary Infection (Altfeld, M) PROJECT 1 DESCRIPTION (provided by applicant): Following viral infections, the first line of defense consists of a highly organized and aggressive innate immune response, while the adaptive immune response, lagging behind, only develops in the context of an active innate immunity. While we have gained extensive knowledge regarding the mechanisms that determine the specificity of the adaptive immune response, very little is known about the mechanisms that determine the recognition of HIV-1 by the innate immune response. However, not only is the innate immune response critical in viral containment at a time when the adaptive immune response is just developing, it is also critical in shaping the function of the subsequent adaptive immune response. Therefore comprehensive studies aimed at deconstructing this early critical arm of the immune response, and its relationship to the adaptive immune response, are necessary to begin to more globally understand the correlates of protective immunity. Since the initial description of pattern recognition receptors, including Toll-like Receptors (TLRs), it has become more and more apparent that these receptors play a crucial role in "sensing" viral infections and initiating the innate immune response directed at the pathogen, and we provide new data demonstrating that HIV-1 encodes for several TLR7/8 ligands. Furthermore, the main cytotoxic effector cells of the innate immune response, NK cells, can specifically recognize virally infected cells via a number cell-specific receptors expressed on their surface. The aim of this proposal is to study the mechanisms by which the effector cells of the innate immune system, and in particular dendritic cells and NK cells, recognize HIV-1 infection and shape the function of the ensuing adaptive antiviral immune response. The following specific aims will be addressed: 1. Assessment of the initiation of the innate immune response by HIV-1-encoded Toll-like receptor ligands, and the impact of innate immune activity on antiviral T cell function. 2. Determine the recognition of HIV-1-infected cells by receptors expressed on NK cells in the acute phase of infection. These studies, which will focus on the recognition of HIV-1 infection by the innate immune system, will provide crucial new insights into HIV-1 pathogenesis, and the earliest events that occur during acute HIV-1 infection that shape the adaptive immune response. The studies assessing the impact of innate immune activation on the quality of the ensuing adaptive virus-specific immune response will furthermore by directly relevant for HIV-1 vaccine design.